As explained in a prior post, neuroscientists made the first real strides in understanding how vision works inside the brain by studying cats. (In short, no matter what we’re looking at, neurons in the primary visual cortex break the image down into line segments, as if the entire world consisted of stick figures.) But the neuroscientists responsible for this work, David Hubel and Torsten Wiesel, also used cats to study brain development, especially during infancy.

For this work, the duo divided a pack of kittens into two cohorts, the horizontal group and the vertical group. As you can probably guess, the vertical group was raised in a world consisting entirely of vertical lines: the wallpaper inside their cages was black-and-white stripes running floor to ceiling, and the people handling and feeding them wore either solid colors or vertical stripes as well. As a result, these cats saw nothing but vertical lines for the first several weeks of their lives. Meanwhile, other cats were raised in cages lined with (and handled by people wearing exclusively) horizontal stripes, and this group never saw vertical lines.

The results was startling. Cats raised in one environment were blind—literally blind—to any lines running the “other” way. Cats raised in a horizontal world, for instance, could see the seats of chairs just fine and would jump up onto them to nap. But they couldn’t see the chair’s legs at all and were constantly banging into them. The vertical-world cats had the opposite problem. They weaved around the chair legs like champs but could never find a cozy spot to snooze.

These experiments provided some of the first and best evidence for the existence of “critical windows” in brain development. The basic idea is that the brain, which is plastic when young, must be exposed to certain sights early in life or it will remain blind to those sights forever. In this case, because the vertical-world and horizontal-world cats never saw any differently oriented lines during their critical windows, their brains ended up dedicating all their vision neurons to the one orientation and neglecting the other.

Something similar can happen with human beings. No humans have ever been raised in such stark surroundings, thankfully. But those of us raised in modern cities tend to notice horizontal and vertical lines more quickly than lines at other orientations. In contrast, people raised in nomadic tribes do a better job noticing lines skewed at intermediate angles, since Mother Nature tends to work with a wider array of lines than most architects. (You wonder, though, where children raised in a city by Gaudi would fall!)

The idea of critical windows extends beyond just vision, of course: almost every system in the brain has a critical window when it needs to experience certain stimuli or it won’t get wired up properly. The most obvious example is language: if you don’t learn a language early on, it’s nigh impossible to become truly fluent. To be sure, different brain systems have different critical windows that last remain open for different lengths of time. But in some fundamental way, we’re all like Hubel and Wiesel’s kittens—able to process some things without effort, but crashing into those darn chair legs that our brains, through no fault of our own, simply can’t process.

(Coming up in part III: “left brain” versus “right brain,” and the Nobel Prize for cats.)

This idea that the infant/child brain has specific windows of time open, that are meant to be stimulated with particular experiences in order to develop properly, is fascinating to me.

I've read of "feral children" who, although they managed to survive somehow without adult care, could not learn to speak. Some could learn to *communicate* in a rudimentary fashion, but that's about it.

There are also the Harlow experiments with infant monkeys, and if I'm remembering correctly, when the adolescent monkeys who had been raised in isolation were introduced to normally-socialized monkeys of the same age for the first time, the isolated ones displayed extreme terror, which generated attack behavior in the normally-socialized monkeys. The isolation-raised "teen" monkeys were better able to tolerate the presence of much younger "child" monkeys, though, which I find really interesting.

I see a possibility that this area of study with the cats' brains could perhaps, eventually, help children who suffer from reactive attachment disorder. RAD children didn't receive neccessary attention or affection from loving caregivers during that crucial "window of time" in their infancy. These children can't "see" love. But if somehow a way could be found to "turn back time" and "reopen the window" in the brain so these children could be exposed to (and their brains could respond the normal way to) loving parental behaviors, then, that would be a wonderful thing.

Sort of along the lines of, if the isolated "horizontal only" and "vertical only" cats were then put in an environment that had mostly *diagonal lines*, might that help their brains *transition* into being able to see ALL line orientations? Similarly to how the isolated monkeys were better able to tolerate the presence of much younger monkeys...

...just "thinking out loud". I think that if researchers from entirely different fields share their studies with each other, that it can have a synergistic, additive effect for all parties.